The present invention relates to a method for checking a value document of a specified type for the suspected presence of a forgery, in particular of a pieced-together forgery, and a device for carrying out the method.
Value documents are understood here to be sheet-shaped objects that represent for example a monetary value or an authorization and hence should not be manufacturable arbitrarily by unauthorized persons. They hence have features that are not simple to manufacture, in particular to copy, whose presence is an indication of authenticity, i.e. manufacture by an authorized body. Important examples of such value documents are chip cards, coupons, vouchers, checks and in particular bank notes. The value documents can respectively differ by their type, for example in the case of bank notes by the denomination or nominal value and the currency, or in the case of checks by a check-form type given by the issuer of the checks.
Forgeries of value documents occasionally appear that will hereinafter also be designated as pieced-together forgeries. They can be formed by connecting a detached part of a value document of a given type—usually by gluing—to a substrate portion, for example a detached part of a value document of a different type or a suitably shaped piece of paper, foil, etc., so as to produce an entity having approximately the dimensions of the value document. In particular, a value document can for example be skillfully divided into two parts which are then respectively joined together with a suitable substrate portion. This results in two forgeries of the value document which are difficult to recognize with simple checking apparatuses, depending on the execution of the forgery. A problem in the machine checking of such value documents is that the glued connection cannot be recognized easily and at the same time reliably.